Double aromaticity: aromaticity in orthogonal planes. The 3,5-dehydrophenyl cation.

We report on novel sandwichlike structures [Al(4)MAl(4)](q-) (q=0-2 and M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W) based on the recently synthesized all-metal aromatic Al(4)(2-) square ring. The sandwichlike structures have two aromatic tetraaluminum square rings which trap a transition-metal cation from either the first, second, or third row. The stability of the anionic sandwichlike complexes towards electron detachment is discussed, and addition of alkali cations is found to stabilize the 2- charged complexes, preventing spontaneous electron detachment. Once the sandwichlike complexes are formed, the Al(4)(2-) square properties remain nearly unchanged; this fact strongly supports the hypothesis that in these complexes the Al(4)(2-) square rings remain aromatic.

Section: Introductionmentioning

confidence: 89%

Sandwich Complexes Based on the “All‐Metal” Al₄²⁻ Aromatic Ring

Mercero

Formoso

Matxain

et al. 2006

“…Boldyrev and co-workers showed that the presence of d atomic orbitals in transition-metal clusters often plays a very important role in determining the chemical behavior of these clusters, which can give rise to d-aromaticity, [51] like in the case of [Ta 3 O 3 ] À . [52] Also, double [53] or multiple aromaticity can exist in transition-metal clusters. For example it was shown that the 1 A' 1 state of the D 3h -symmetric Hf 3 cluster is triply (s, p, and d) aromatic.…”

Section: /1pmentioning

confidence: 99%

Growth Mechanism and Chemical Bonding in Scandium‐Doped Copper Clusters: Experimental and Theoretical Study in Concert

Höltzl

Veldeman

Haeck

et al. 2009

Size matters! The electronic structure and size-dependent stability of neutral and cationic scandium-doped copper clusters have been investigated by mass spectrometric studies (for the cations) and also quantum chemical computations. The proposed reaction paths ultimately lead to the most stable Frank-Kasper-shaped Cu(16)Sc(+) cluster (shown here), which could be the germ of a new crystallization process.Electronic structure and size-dependent stability of scandium-doped copper cluster cations, Cu(n)Sc(+), were investigated by using a dual-target dual-laser vaporization production scheme followed by mass spectrometric studies and also quantum chemical computations in the density functional theory framework. The neutral species also were studied by using computational methods. Enhanced abundances and dissociation energies were measured in the case of Cu(n)Sc(+) for n=4, 6, 8, 10 and 16, the last of these identified as being extraordinary stable. Neutral clusters are stable with n=5, 7, 9 and 15, which are isoelectronic with respect to the number of the valence s electrons with the stable cationic clusters; hence a simple electron count determines cluster properties to a great extent. The Cu(17)Sc cluster was found to be a superatomic molecule, containing Cu(16)Sc(+) and Cu(-) units; however, the charge separation is not as pronounced as in the case of CuLi. Cu(15)Sc was found to be a stable cluster with a large dissociation energy and a closed electronic structure; hence this can be regarded as a superatom, analogous to the noble gases. The main factors determining the growth patterns of these clusters are the central position of the scandium atom and the successive filling of the shell orbitals. For smaller clusters, the reaction paths appear to diverge yielding various products; however all paths ultimately lead to the most stable Frank-Kasper shaped Cu(16)Sc cluster, which in turn can be the germ of the crystallization process.

“…Double aromaticity, as originally conceived by Chandrasekhar, Jemmis, and Schleyer in 1979, [1] is defined as the existence of two mutually orthogonal cyclically delocalized electronic systems in a single molecule, both of which provide significant stabilization. Thus, the usual Hückel 4n+2 p electron system, comprised of p AOs perpendicular to a ring, may be augmented by an in-plane 4n+2 electron system comprised of radial (rad; inward-pointing) p AOs.…”

Section: Introductionmentioning

confidence: 99%

Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

Wodrich

Corminbœuf

Schleyer

2007

The double-aromatic character of selected monocyclic carbon, boron, and borocarbon rings is demonstrated by refined nucleus-independent chemical shift (NICS) analyses involving the contributions of individual canonical MOs and their out-of-plane NICS tensor component (CMO-NICS(zz)). The double aromaticity considered results from two mutually orthogonal Hückel p AO frameworks in a single molecule. The familiar pi orbitals are augmented by the in-plane delocalization of electrons occupying sets of radial (rad) p orbitals. Such double aromaticity is present in B(3) (-), C(6)H(3) (+), C(6) (4+), C(4)B(4) (4+), C(6), C(5)B(2), C(4)B(4), C(2)B(8), B(10) (2-), B(12), C(10), C(9)B(2), C(8)B(4), C(7)B(6), C(6)B(8), and C(14). Monocyclic C(8) and C(12) are doubly antiaromatic, as both the orthogonal pi and radial Hückel sets are paratropic. Planar C(7) and C(9) monocycles have mixed aromatic (pi) and antiaromatic (radial) systems.